среда, 3 июня 2009 г.

Add protection means add “a hole”

Funny news

New D-Link protection for Wi-Fi routers is a hole in security!

D-Link had barely announced updated firmware for wireless routers with protection from automatic registrations (CAPTCHA), when several enthusiasts found out that this new protection measures make routers more vulnerable to password theft.

The situation is much more amusing, indeed. The problem is that CAPTCHA is used by D-Link to protect from Cross-Site Request Forgery (CSRF) which (to be more precise, exploitation method for a router) was greatly named Drive-by Pharming by Symantec. But implementation error (accepting of requests with valid hash without CAPTCHA) makes this protection to be a vulnerability.

But if the password (or its derivative such as hash) is sent to GET (as Basic duplicate), then the situation is more interesting – an attacker could use not only standard password hash but also conduct user password brute force attack Javascript via CSRF from which CAPTCHA should protect.

It means that the vulnerability concerns not only standard passwords but also could increase the effectiveness of user password brute force attacks via CSRF, and standard password security (timeout, temporary lockout, etc.) does not work as not brute force itself but attempts to connect with different “normal” hashes are taken, used instead of session identifier. A simple script is enough for it, that call the address

GET /post_login.xml?hash=

and check whether the action was successful. The point is to trick a user to open the site:)

In general, rather interesting design error in authentication mechanism of web application.